1. Field of the Invention
The present invention relates to: a control system for performing a data reading/writing process for one storage device while performing a data erasing process for another storage device simultaneously and in parallel by switching the connection status between a plurality of storage devices and a control apparatus; a control apparatus and a storage device to be used in such a control system; and a computer program product for such a control system.
2. Description of Related Art
An image forming apparatus such as a digital multi function printer for temporarily storing electronic document data in a storage unit thereof and processing the data is widely used. A digital multi function printer comprises a scanner for reading an original image and a printer unit for forming an image on a paper, and has a plurality of functions such as a copying function, a facsimile function, a scanner function and a printing function. Such a digital multi function printer proposes to the user advancement of availability and performance when being located on a communication network as a data processing device for efficiently processing data inputted from a plurality of interfaces. A digital multi function printer is also equipped with a mass storage device such as a hard disk for enabling rapid processing of various mass data, so that a plurality of data process requests can be accepted and data can be sequentially processed.
In such a storage device such as a hard disk, data is temporally written and held for processing. When data is newly inputted after completion of the process, data which has been already processed is erased by overwriting meaningless data to accept new data. Accordingly, there is a problem from the perspective of data protection since data which has been processed is let stand in the device until new data is written. In these circumstances, a device which erases and invalidates data which has been processed has been invented in recent years in order to avoid data from being let stand in the device (for example, see Japanese Patent Application Laid-Open No. 9-284572 (1997)).
Regarding an image forming apparatus or the like equipped with a storage device for repeatedly and sequentially performing a data writing process and a data erasing process as described above, it is required to enhance the access rate of the storage device in order to enhance the performance of the entire system. Proposed as technology for enhancing the access rate of the storage device are: a device using a disk array device constructed with the RAID (Redundant Arrays of Inexpensive Disks) in conjunction with a write cache (see Japanese Patent Application Laid-Open No. 2000-305717); and a device for enhancing the access rate by equipping the hard disk itself with a plurality of heads (see Japanese Patent Application Laid-Open No. 63-18580 (1988) and Japanese Patent Application Laid-Open No. 5-205285 (1993)).
However, the device disclosed in Japanese Patent Application Laid-Open No. 2000-305717, which has only one means for accessing a disk in the device, has a problem that it is required to prioritize any one access over the other when an access by a normal reading process and a normal writing process and an access for a data erasing process are made simultaneously and lowering of the entire apparent disk access rate cannot be prevented.
Moreover, the device disclosed in Japanese Patent Application Laid-Open No. 63-18580 (1988), which has a commonly used bus to be connected with the hard disk and the system, has a problem that an access for a reading process and a writing process collides with an access for an erasing process at the bus portion and lowering of the disk access rate cannot be prevented.
Moreover, the device disclosed in Japanese Patent Application Laid-Open No. 5-205285 (1993), which has two heads at a disk and one bus for one head, can make an access for a reading process and a writing process and an access for an erasing process with different heads, so that no collision arises between the two accesses. However, such a device has a problem that it is expensive since a hard disk having two heads and two buses is a specialized disk.